The present invention relates to a phoropter for testing the visual acuity of a test person.
Phoropters are known in the most widely varying embodiments. Thus a phoropter is known with a rotating knob device for the selection of certain types of function of said device, in particular an electronic phoropter, by setting or adjusting a rotating part that is rotatable about an axis of rotation to certain positions defined by the angular position vis-a-vis a basic part.
These phoropters are actuated by turning mechanical switches into angular positions defined by mechanical engagement click stops. Such phoropters require a substantial amount of space and, particularly on account of the friction connected with the mechanical engagement, are difficult to operate.
Furthermore, a phoropter with several lens disks rotatably supported on at least one spindle in a frame and with a circular indicating means for the angular position of the shaft position of a cylinder component (cylinder shaft) of the optical system swung or swiveled into the light path, which is mounted so as to be rotatable about a setting spindle is known. In a phoropter known e.g. from the DE-PS 29 01 459, a plurality of lens disks is arranged in series, while on at least one disk, cylinder or crossed cylinder lenses may be disposed which each are rotatable about a setting spindle in order to be able in this way to change the angular position of the cylinder component. The angular position of the cylinder spindle lying transversely to the light beam axis or to the viewing direction can be read off from a scale graduation on the side facing the examining ophthalmologist. Due to the poor room illumination this causes considerable difficulties and may possibly lead to errors being committed. The indication and reading off may also be carried out on a keyboard console which is accordingly better illuminated and separated from the phoropter. This is inconvenient because the examining party is thus compelled to look in a different direction than that of the patient.
A further apparatus for testing the visual acuity of a test person (phoropter) is protected against the environment by a covering (housing). Furthermore, a forehead rest for positioning the head of the test person is attached to a frame and, for each eye, a stack holder or support, on which, rotatable about an approximately horizontal spindle, a stack of disks each is disposed which, in circular arrangement, carry a plurality of optical elements, more particularly, spherical and cylindrical lenses, of which one each of every disk is turned in front of a viewing aperture, the shaft of the one stack being, relative to the shaft of the other stack, adjusted vertically and, if necessary, swivelable for viewing a close-up reading test specimen. In apparatuses of this type, adjusting means are necessary on the disks of the optical elements, but also for the setting up of the stacks, said adjusting means being manually operated. For this purpose, the apparatus is provided with a number of openings through which, in the course of time, dust and other dirt particles penetrate which may particularly impair the surfaces of the lenses as well. When the housing covers all the component parts, it creates a shapeless and voluminous impression. When individual subassemblies are disposed so as to be separated from each other and actuating elements, e.g. rotating knobs, are mounted on the outside, an irregular impression is created and the mechanical linkages between the apparatus components likewise detrimentally affect the appearance and are prone to mechanical damage or to contamination.
It is the object of the invention to be able, in a phoropter, to effect the selection of the types of function without mechanical switches or the like that are directly connected to the device and to also simplify the click stop engagement by means of a minor structural expenditure. Moreover, it is the object of the invention to improve the indication of the angularity of a cylinder component of the phoropter and to facilitate, for the examining party, the obtaining of an immediate stereoscopic impression regarding the position of the shaft in relation to the eye to be examined. In addition, it is intended to construct a phoropter in such a compact manner that the parts to be moved will, if possible, all be covered and thus protected against extraneous effects and that, this notwithstanding, an overall tranquil and harmonious impression exists.